1. Field of the Invention
The present invention relates to a stabilization formulation for stabilizing polyolefins from ultraviolet degradation and to the polyolefin compositions containing the formulation.
2. Related Art
High molecular weight polymers obtained by the polymerization of terminally unsaturated monoolefins, such as polyethylene, polypropylene, polybutene-1 and the like, have found wide and varied uses, replacing many conventional materials and creating new uses. Basically the polymers have many attractive physical properties that led to their initial acceptance, and by continuous search for compounding aids and additives these properties have been improved. For example, U.S. Pat. Nos. 3,361,852; 3,433,573 and 4,210,597 all disclose compounding polyolefins with ethylene vinyl acetate to obtain improved physical properties. However, the polymers are to varying degrees unstable in regard, for example, to oxidation and to ultraviolet radiation. Thus, stabilizer(s) are almost always added to polyolefins and blends thereof to provide protection against unwanted oxidation and ultraviolet degradation.
Polypropylene has especially desirable properties for outside applications, such as, a replacement for natural hemp in ropes and twine, however, polypropylene is particularly subject to ultraviolet light degradation. Many materials have been suggested and employed as UV stabilizers for polyolefins, such as hindered amines, benzophenones, benzotriazoles, salicylates, nickel dialkyldithiocarbamates and the like.
It has now been found that a formulation comprising specific known stabilizers in combination with a specific type of ethylene vinyl acetate copolymer provides surprising and synergistic stability for polyolefins against ultraviolet light degradation. Until the present invention, ethylene vinyl acetate copolymer, has not been considered in any regard as having significant effect on UV stability. Indeed, ethylene vinyl acetate copolymers have been employed with polyolefins primarily to improve impact strength and low temperature characteristics of the polyolefins.
It is an advantage of the present invention that the components of the UV stabilizing formulation have been used with the polyolefins and are generally compatible therewith, without detriment to other properties. It is a further advantage that the blending of the UV stabilizing system with the polyolefins is carried out by known and conventional equipment and methods. It is a feature that the polyolefin compositions containing the UV stabilizer system are superior in UV stability.